Compact lost motion system for variable value actuation

ABSTRACT

Lost motion systems and methods for providing engine valves with variable valve actuation for engine valve events are disclosed. The system may include a master piston hydraulically linked to a slave piston, and a dedicated cam operatively connected to the master piston. The slave piston may be disposed substantially perpendicular to the master piston in a common housing. The slave piston is adapted to actuate one or more engine valves. The slave piston may incorporate an optional valve seating assembly into its upper end. A trigger valve may be operatively connected to the master-slave hydraulic circuit to selectively release and add hydraulic fluid to the circuit.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation in part of, relates to, and claimsthe priority of U.S. patent application Ser. No. 10/408,254 filed Apr.8, 2003, which relates to and claims priority on U.S. provisional patentapplication Ser. No. 60/370,249 which was filed Apr. 8, 2002.

FIELD OF THE INVENTION

The present invention relates generally to a system and method foractuating a valve in an internal combustion engine. In particular, thepresent invention relates to a system and method that may providevariable actuation of intake, exhaust, and auxiliary valves in aninternal combustion engine, and may provide a fail safe method so thatthe engine may be operated without damage in the event of a componentfailure.

BACKGROUND OF THE INVENTION

Valve actuation in an internal combustion engine is required in orderfor the engine to produce positive power. During positive power, one ormore intake valves may be opened to admit fuel and air into a cylinderfor combustion. One or more exhaust valves may be opened to allowcombustion gas to escape from the cylinder. Intake, exhaust, and/orauxiliary valves also may be opened during positive power at varioustimes to recirculate gases for improved emissions.

Engine valve actuation also may be used to produce engine braking andexhaust gas recirculation (EGR) when the engine is not being used toproduce positive power. During engine braking, the exhaust valves may beselectively opened to convert, at least temporarily, the engine into anair compressor. In doing so, the engine develops retarding horsepower tohelp slow the vehicle down. This can provide the operator with increasedcontrol over the vehicle and substantially reduce wear on the servicebrakes of the vehicle.

In many internal combustion engines, the intake and exhaust valves maybe opened and closed by fixed profile cams, and more specifically by oneor more fixed lobes that are an integral part of each of the cams.Benefits such as increased performance, improved fuel economy, loweremissions, and better vehicle driveablity may be obtained if the intakeand exhaust valve timing and lift can be varied. The use of fixedprofile cams, however, can make it difficult to adjust the timingsand/or amounts of engine valve lift in order to optimize them forvarious engine operating conditions, such as different engine speeds.

One proposed method of adjusting valve timing and lift, given a fixedcam profile, has been to provide variable valve actuation byincorporating a “lost motion” device in the valve train linkage betweenthe valve and the cam. Lost motion is the term applied to a class oftechnical solutions for modifying the valve motion proscribed by a camprofile with a variable length mechanical, hydraulic, or other linkageassembly. In a lost motion system, a cam lobe may provide the “maximum”(longest dwell and greatest lift) motion needed over a full range ofengine operating conditions. A variable length system may then beincluded in the valve train linkage, intermediate of the valve to beopened and the cam providing the maximum motion, to subtract or losepart or all of the motion imparted by the cam to the valve.

This variable length system (or lost motion system) may, when expandedfully, transmit all of the cam motion to the valve, and when contractedfully, transmit none or a minimum amount of the cam motion to the valve.An example of such a system and method is provided in Hu, U.S. Pat. Nos.5,537,976 and 5,680,841, which are assigned to the same assignee as thepresent application and which are incorporated herein by reference.

In the lost motion system of U.S. Pat. No. 5,680,841, an engine camshaft may actuate a master piston which displaces fluid from itshydraulic chamber into a hydraulic chamber of a slave piston. The slavepiston in turn acts on the engine valve to open it. The lost motionsystem may include a solenoid trigger valve in communication with thehydraulic circuit that includes the chambers of the master and slavepistons. The solenoid valve may be maintained in a closed position inorder to retain hydraulic fluid in the circuit when the master piston isacted on by certain of the cam lobes. As long as the solenoid valveremains closed, the slave piston and the engine valve respond directlyto the hydraulic fluid displaced by the motion of the master piston,which reciprocates in response to the cam lobe acting on it. When thesolenoid is opened, the circuit may drain, and part or all of thehydraulic pressure generated by the master piston may be absorbed by thecircuit rather than be applied to displace the slave piston and theengine valve.

Previous lost motion systems have typically not utilized high speedmechanisms to rapidly vary the length of the lost motion system,although the aforementioned '841 patent does contemplate the use of ahigh speed trigger valve. High speed lost motion systems in particular,are needed to provide Variable Valve Actuation (VVA). True variablevalve actuation is contemplated as being sufficiently fast as to allowthe lost motion system to assume more than one length within theduration of a single cam lobe motion, or at least during one cycle ofthe engine. By using a high speed mechanism to vary the length of thelost motion system, sufficiently precise control may be attained overvalve actuation to enable more optimal valve actuation over a range ofengine operating conditions. While many devices have been suggested forrealizing various degrees of flexibility in valve timing and lift, lostmotion hydraulic variable valve actuation is becoming recognized forsuperior potential in achieving the best mix of flexibility, low powerconsumption, and reliability.

Engine benefits from lost motion VVA systems can be achieved by creatingcomplex cam profiles with extra lobes or bumps to provide auxiliaryvalve lifts in addition to the conventional main intake and exhaustevents. Many unique modes of engine valve actuation may be produced by aVVA system that includes multi-lobed cams. For example, an intake camprofile may include an additional lobe for EGR prior to the main intakelobe, and/or an exhaust cam profile may include an additional lobe forEGR after the main exhaust lobe. Other auxiliary lobes for cylindercharging, and/or compression release may also be included on the cams.The lost motion VVA system may be used to selectively cancel or activateany or all combinations of valve lifts possible from the assortment oflobes provided on the intake and exhaust cams. As a result, significantimprovements may be made to both positive power and engine brakingoperation of the engine.

The foregoing benefits are not necessarily limited to exhaust and intakevalves. It is also contemplated by the present inventors that lostmotion VVA may be applied to an auxiliary engine valve that is dedicatedto some purpose other than intake or exhaust, such as for example enginebraking or EGR. By providing an auxiliary engine valve cam with all ofthe possible actuations that may be desired and a lost motion VVAsystem, the actuation of the auxiliary valve may be varied foroptimization at different engine speeds and conditions.

In view of the foregoing, the lost motion system and method embodimentsof the present invention may be particularly useful in engines requiringvariable valve actuation for positive power, engine braking valve events(such as, for example, compression release braking), and exhaust gasrecirculation valve events.

Each of the foregoing types of valve events (main intake, main exhaust,engine braking, and exhaust gas recirculation) occur as a result of anengine valve being pushed into an engine cylinder to allow the flow ofgases to and from the cylinder. Each event inherently has a starting(opening) time and an ending (closing) time, which collectively definethe duration of the event. The starting and ending times may be markedrelative to the position of the engine (usually the crankshaft position)at the occurrence of each. These valve events also inherently include apoint at which the engine valve reaches its maximum extension into theengine cylinder, which is commonly referred to as the valve lift. Thus,each valve event can be defined, at least at a basic level, by itsstarting and ending time, and the valve lift.

If the lost motion system connecting the engine cam to the engine valvehas a fixed length each time a particular lobe acts on the system, thenthe starting and ending times and the lift for each event marked by thatlobe will be fixed. Furthermore, a lost motion system that has a fixedlength over the duration of the entire cam revolution will produce avalve event in response to each lobe on the cam, assuming that thesystem does not incorporate a lash space between the lost motion systemand the engine valve. The optimal starting time, ending time, and liftof an engine valve is not “fixed,” however, but may differ widely fordifferent engine operating modes (e.g., different engine load, fueling,cylinder cut-out, etc.), for different engine speeds, and for differentenvironmental conditions. Accordingly, it is desirable to have a lostmotion system that is not fixed in length, but rather “variable” overthe short run, where the short run is as brief as the duration of timeit takes for a cam lobe to pass a fixed point (i.e. as little as a fewcam shaft rotation degrees), or at least no longer than one cam shaftrevolution.

It is also desirable to provide optimal power and fuel efficiency duringpositive power operation of an engine. One advantage of variousembodiments of the present invention is that they may be used to varythe intake and exhaust valve timing and/or lift to provide optimal powerand fuel efficiency, if so desired. The use of a lost motion VVA systemallows valve timing and/or lift to be varied in response to changingengine conditions, load and speed. These variations may be made inresponse to real-time sensing of engine conditions and/or pre-programmedinstructions.

It is also desirable to reduce NOx and/or other polluting emissions fromthe exhaust of internal combustion engines, and diesel engines inparticular. One advantage of various embodiments of the presentinvention is that they may be used to reduce NOx and other pollutingemissions by carrying out internal exhaust gas recirculation or trappingresidual exhaust gas using variable valve timing and auxiliary lifts ofintake, exhaust, and/or auxiliary valves. By allowing exhaust gas todilute the incoming fresh air charge from the intake manifold, lowerpeak combustion temperatures may be achieved without large increases infuel consumption, which may result in less formation of pollution andmore complete burning of hydrocarbons.

Also of great interest for diesel engines is the capability of theengine to have an engine braking mode. It is another advantage ofvarious embodiments of the present invention to optimize engine brakingacross an engine speed range, as well as modulate engine brakingresponsive to driver demand.

It is also desirable to provide engines with the ability to warm upfaster by employing special valve timing during a brief period after theengine is started. Driver comfort and after-treatment deviceefficiencies may depend on how quickly an engine can be brought up tonormal operating temperature. Yet another advantage of variousembodiments of the present invention is that they may provide improvedengine warm up. This can be achieved using a number of differenttechniques, including, but not limited to, early intake valve closing,EGR, changes in exhaust/intake valve overlap, cylinder cut-out of somecylinders, and even compression release braking of some cylinders duringpositive power to effectively make the engine work against itself.

The ability to provide cylinder cut-out may be useful not only duringengine warm-up and not only for diesel engines. In some embodiments ofthe present invention, the lost motion VVA system may be adapted to loseall cam motions associated with an engine valve or even an enginecylinder. As a result, these lost motion VVA systems may be used toeffectively “cut-out” or shut off one or more engine cylinders frominclusion in the engine. This ability may be used to vary the number ofcylinders that fire during positive power, to add control over fuelefficiency and power availability. Cylinder cut-out may also increaseexhaust gas temperature in the cylinders that continue to fire, therebyimproving the efficiency of exhaust after-treatment. It is alsocontemplated that cylinder cut-out could be carried out sequentially atthe time an engine is turned on and/or off to decrease the amount of outof balance shake that is produced by an engine during start-up andshut-down periods.

However, having a hydraulic circuit with various valves transferringmotion from a cam or other motion imparting device to an engine valvemay possess an increased risk of valve or engine damage or enginefailure in the event a solenoid or trigger valve fails. In such afailure situation, the VVA system may be disabled such that the enginevalves associated with the VVA system do not open or close as desired.This may result in engine failure. Further, in a failure situation theVVA system may be disabled with an engine valve in an open position.Such a position may lead to valve or engine damage due to valve-pistoncontact. Thus, a VVA system with a fail-safe attribute may be desirable.

Further, a hydraulic circuit for transferring motion from a cam or othermotion imparting device to an engine valve may cause problems for enginevalve actuation during start-up and warm-up. This is because hydraulicfluid may drain from the hydraulic circuit as the engine sits in a stateof non-use. When the engine is started, the hydraulic circuit betweenthe cam and engine valves may be empty, and therefore the valve may notbe actuated. Thus, a secondary method of actuating the engine valvesduring start-up or warm-up is desirable.

Space and weight considerations are also of considerable concern toengine manufacturers. Accordingly it is desirable to reduce the size andweight of the engine subsystems responsible for valve actuation. Someembodiments of the present invention are directed towards meeting theseneeds by providing a compact master-slave piston housing for the lostmotion VVA system. Applicants have discovered that some unexpectedadvantages may also be realized by reducing the size of the lost motionVVA system. As a result of reduction of the overall size of the system,the attendant hydraulic passages therein may be reduced in volume, thusimproving hydraulic compliance.

Additional advantages of the invention are set forth, in part, in thedescription that follows and, in part, will be apparent to one ofordinary skill in the art from the description and/or from the practiceof the invention.

SUMMARY OF THE INVENTION

Applicants have developed an innovative lost motion system that iscapable of providing variable valve actuation. The system may include amaster and slave piston circuit in communication with a high speedtrigger valve. Selective actuation of the trigger valve may be used toprovide a wide range of engine valve events of different durations andlifts.

Applicants have also developed an innovative lost motion valve actuationsystem comprising: a housing having a master piston bore and a slavepiston bore, wherein the master piston bore and the slave piston boresintersect; a master piston slidably disposed in the master piston bore,wherein the master piston is adapted to receive an input motion; and aslave piston slidably disposed in the slave piston bore, wherein theslave piston is adapted to actuate one or more engine valves.

Applicants have further developed an innovative system for providingengine valves with variable valve actuation for engine valve events,said system comprising: a housing having a master piston bore and aslave piston bore; a master piston slidably disposed in the masterpiston bore; a cam operatively connected to the master piston, said camdedicated to operation of the master piston; a slave piston slidablydisposed in the slave piston bore, wherein the slave piston isselectively hydraulically linked to the master piston and adapted toactuate one or more engine valves; a valve seating assembly incorporatedinto the slave piston; and a trigger valve operatively connected to theslave piston bore.

Applicants have further developed an innovative lost motion valveactuation system comprising: a housing having a master piston bore and aslave piston bore, wherein the master piston bore and the slave pistonbore extend axially in directions substantially perpendicular to eachother; a master piston slidably disposed in the master piston bore,wherein the master piston is adapted to receive an input motion; and aslave piston slidably disposed in the slave piston bore, wherein theslave piston is adapted to actuate one or more engine valves.

Applicants have further developed an innovative system that provides afail-safe attribute to a VVA system, said system comprising a housinghaving a master piston bore and a slave piston bore; a master pistonslidably disposed in the master piston bore; a slave piston slidablydisposed in the slave piston bore, wherein the slave piston isselectively hydraulically linked to the master piston and adapted toactuate one or more engine valves; a motion imparting device; a rockerarm pivotally disposed on a rocker shaft, wherein the rocker arm isadapted to receive motion from the motion imparting device and transfersaid motion to the master piston; and a trigger valve operativelyconnected to the slave piston bore.

Applicants have further developed a second innovative system thatprovides a fail-safe attribute to a VVA system, said system comprisingat least one engine valve; a housing having a master piston bore and aslave piston bore; a master piston slidably disposed in the masterpiston bore; a slave piston slidably disposed in the slave piston bore,wherein the slave piston is selectively hydraulically linked to themaster piston and adapted to actuate one or more engine valves; a motionimparting device; a first rocker arm and second rocker arm pivotally andcoaxially disposed on a rocker shaft, wherein the first rocker arm isadapted to receive motion from the motion imparting device and transfersaid motion to the master piston and to the second rocker arm, andwherein the second rocker arm receives said motion from the first rockerarm; and a trigger valve operatively connected to the slave piston bore.

Applicants have still further developed an innovative method ofproviding variable valve actuation for an internal combustion enginevalve using a slave piston hydraulically linked to a master piston forall non-failure mode valve actuations carried out by the engine valve,said method comprising the steps for: displacing the master piston in amaster piston bore responsive to a cam motion; providing hydraulic fluidto a slave piston bore directly from the master piston bore responsiveto displacement of the master piston; displacing the slave piston in theslave piston bore responsive to the provision of hydraulic fluid to theslave piston bore; actuating the engine valve responsive to displacementof the slave piston; and selectively releasing hydraulic fluid from andadding hydraulic fluid to the slave piston bore to achieve variablevalve actuation.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory only,and are not restrictive of the invention as claimed. The accompanyingdrawings, which are incorporated herein by reference, and whichconstitute a part of this specification, illustrate certain embodimentsof the invention and, together with the detailed description, serve toexplain the principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to assist the understanding of this invention, reference willnow be made to the appended drawings, in which like reference charactersrefer to like elements. The drawings are exemplary only, and should notbe construed as limiting the invention.

FIG. 1 is a block diagram of a valve actuation system according to afirst embodiment of the present invention.

FIG. 2 is a schematic diagram of a valve actuation system according to asecond embodiment of the present invention.

FIG. 3 is a schematic diagram of a valve actuation system according to athird embodiment of the present invention.

FIG. 4 is a schematic diagram of a cam having multiple lobes for use inconnection with various embodiments of the present invention.

FIG. 5 is a schematic diagram of a valve actuation system according to afourth embodiment of the present invention.

FIG. 6 is a schematic diagram of an alternative embodiment of theinvention in which a bleeder braking hydraulic plunger is integratedinto a lower portion of the system housing.

FIG. 7 is a schematic diagram of another alternative embodiment of theinvention including means for limiting the accumulator volume to providea limp-home mode of operation.

FIG. 8 is a schematic diagram of the upper slave piston region, and morespecifically the valve seating assembly, shown in FIG. 7.

FIG. 9 is a schematic diagram of another alternative embodiment of thepresent invention including a clipping passage for the slave piston.

FIG. 10 is a graph of engine valve lift verses crank angle illustratingconventional positive power main intake and exhaust valve motions.

FIG. 11 is a graph of engine valve lift verses crank angle illustratingpositive power centered lift main intake and exhaust valve motions.

FIG. 12 is a graph of engine valve lift verses crank angle illustratingearly intake valve closing during positive power operation.

FIG. 13 is a graph of engine valve lift verses crank angle illustratingintake and exhaust valve EGR events carried out in conjunction withearly intake valve closing during positive power operation.

FIG. 14 is a graph of engine valve lift verses crank angle illustratingbleeder braking.

FIG. 15 is a graph of engine valve lift verses crank angle illustratingcompression release engine braking valve motions.

FIG. 16 is a graph of engine valve lift verses crank angle illustratingearly exhaust valve opening during positive power operation.

FIG. 17 is a schematic diagram of a valve actuation system in accordancewith an embodiment of the present invention.

FIG. 18 is a schematic diagram of a valve actuation system in accordancewith an embodiment of the present invention.

FIG. 19 is a schematic diagram of a valve actuation system in accordancewith an embodiment of the present invention.

FIG. 20 is a cross section of a valve seating device in accordance withan embodiment of the present invention.

FIG. 21 is a graph depicting a valve profile, in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

As embodied herein, the present invention includes both systems andmethods of controlling the actuation of engine valves. Reference willnow be made in detail to a first embodiment of the present invention, anexample of which is illustrated in the accompanying drawings. A firstembodiment of the present invention is shown in FIG. 1 as valveactuation system 10. The valve actuation system 10 includes a means forimparting motion 100 (motion means) connected to a lost motion system200, which in turn is connected to one or more engine valves 300. Themotion imparting means 100 provides an input motion to the lost motionsystem 200. The lost motion system 200 may be selectively switchedbetween modes of: (1) losing the motion input by the motion means 100,and (2) transferring the input motion to the engine valves 300. Themotion transferred to the engine valves 300 may be used to producevarious engine valve events, such as, but not limited to, main intake,main exhaust, compression release braking, bleeder braking, externaland/or internal exhaust gas recirculation, early exhaust valve opening,early intake closing, centered lift, etc. The valve actuation system 10,including the lost motion system 200, may be switched between a mode oflosing motion and that of not losing motion in response to a signal orinput from a controller 400. The engine valves 300 may be exhaustvalves, intake valves, or auxiliary valves.

The motion imparting means 100 may comprise any combination of cam(s),push tube(s), and/or rocker arm(s), or their equivalents. The lostmotion system 200 may comprise any structure that connects the motionimparting means 100 to the valves 300 and is capable of selectivelytransmitting motion from the motion imparting means 100 to the valves300. In one sense, the lost motion system 200 may be any structurecapable of selectively attaining more than one fixed length. The lostmotion system 200 may comprise, for example, a mechanical linkage, ahydraulic circuit, a hydro-mechanical linkage, an electromechanicallinkage, and/or any other linkage adapted to connect to the motionimparting means 100 and attain more than one operative length. When itincorporates a hydraulic circuit, the lost motion system 200 may includemeans for adjusting the pressure, or amount of fluid in the circuit,such as, for example, trigger valve(s), check valve(s), accumulator(s),and/or other devices used to release hydraulic fluid from or addhydraulic fluid to a circuit. The lost motion system 200 may be locatedat any point in the valve train connecting the motion imparting means100 and the valves 300.

The controller 400 may comprise any electronic or mechanical device forcommunicating with the lost motion system 200 and causing it to eitherlose some or all of the motion input to it, or not lose this motion. Thecontroller 400 may include a microprocessor, linked to other enginecomponents, to determine and select the appropriate instantaneous lengthof the lost motion system 200. Valve actuation may be optimized at aplurality of engine speeds and conditions by controlling theinstantaneous length of the lost motion system 200 based uponinformation collected by the microprocessor from engine components.Preferably, the controller 400 is adapted to operate the lost motionsystem 200 at high speed (one or more times per engine cycle).

Another embodiment of the present invention is illustrated in FIG. 2.With reference thereto, the motion imparting means 100 may comprise acam 110, a rocker arm 120, and a push tube 130. With reference to FIG.4, the cam 110 may optionally include one or more lobes, such as a main(exhaust or intake) event lobe 112, an engine braking lobe 114, and anEGR lobe 116. The depictions of the lobes on the cam 110 are intended tobe illustrative only, and not limiting. It is appreciated that thenumber, size, location, and shape of the lobes may vary markedly withoutdeparting from the intended scope of the invention.

With continued reference to FIG. 2, the cam 110 acts on the rocker arm120. The rocker arm 120 may include a central opening 122 for receipt ofa rocker shaft, and a cam follower 124. The rocker arm 120 is adapted topivot back and forth about the central opening 122. Lubrication for therocker arm 120 may be provided through the rocker shaft inserted intothe central opening 122. The rocker arm 120 may also include a socket126 for receipt of an end of the push tube 130. The socket may bedesigned to allow some pivot motion as the rocker arm 120 acts on thepush tube 130.

The lost motion system 200 may include a housing 202, a master piston210, a master-slave hydraulic circuit 220, a slave piston 230, anaccumulator 250, and a trigger valve 260. The housing 202 may include abore for receiving the master piston 210, a bore for receiving the slavepiston 230, a bore 254 for receiving the accumulator, and a bore forreceiving the trigger valve 260. The hydraulic circuit 220 is providedin the housing 202 and may connect the master piston 210, the slavepiston 230, the trigger valve 260, and the accumulator 250. Hydrauliccommunication between the accumulator 250 and the other elements in thelost motion system may be controlled by using the trigger valve 260 toselectively open and close communication between the hydraulic circuit220 and the passage 222 that extends between the trigger valve and theaccumulator.

The master piston 210 may be disposed in a bore in the housing 202 suchthat it can slide back and forth in the bore while maintaining ahydraulic seal with the housing. It is anticipated that some leakagearound this seal will not affect the operation of the lost motion system200. The master piston 210 may include an interior socket 214 forreceipt of a second end of the push tube 130. The end of the push tube130 and the socket within the master piston 210 may be shaped tocooperate and permit a slight pivoting motion relative to each other.The master piston 210 may also include an outer flange 216 adapted tomate with a master piston spring 212. The master piston spring 212 mayact on the flange 216 so as to bias the master piston 210 toward therocker arm through the push tube 130. In turn, the rocker arm 120 isbiased into the cam 110.

The master piston 210 may be disposed in the housing 202 in a directionsubstantially orthogonal or perpendicular to the orientation of theengine valves 300 and the slave piston 230. The master piston 210 boreand the slave piston 230 bore may have a short or zero fluid linelengths between them in various embodiments of the present invention.Master and slave piston bores with short or zero fluid line lengths mayactually intersect, as shown in FIG. 2. The orthogonal orientation ofthe master piston 210, and the zero or near zero fluid line lengthbetween the master piston and slave piston bores, may enable the lostmotion system 200 to be more compact than it might otherwise be. As aresult hydraulic compliance challenges may be overcome by employingreduced hydraulic volumes. Thus, the orthogonal relationship of themaster piston 210 and the slave piston 230 may provide a uniqueopportunity to both “save space” in the engine compartment, and providethe master and slave pistons in very close proximity.

The slave piston 230 may be slidably disposed in a bore in the housing202 in an orientation substantially parallel with that of the enginevalves 300. As shown in FIG. 2, the slave piston 230 acts on a valvebridge 310 associated with the engine valves 300. It is appreciated thatthe slave piston 230 could act directly on one or more engine valves inalternative embodiments of the invention.

The slave piston 230 may be selected to have a diameter of a selectedproportion to that of the master piston 210. The relationship of thesetwo diameters affects the relationship of the linear displacement of theslave piston 230 that occurs as a result of linear displacement of themaster piston 210 given the hydraulic circuit connecting the two isclosed. The ratio of the linear displacement of the master piston 210 tothe resultant linear displacement of the slave piston 230 may bereferred to as the hydraulic ratio of the pistons. It is appreciatedthat the optimal hydraulic ratio may vary in accordance with thespecifications of the engine in which the lost motion system 200 isprovided. The system 10 may employ a master piston 210 with an equal,larger, or smaller diameter compared to the slave piston 230. When theslave piston diameter is smaller, its stroke may be longer than that ofthe associated master piston. The preferred hydraulic ratio of themaster piston to the slave piston may be in the range of 0.5 to 2.

The slave piston 230 may incorporate a valve seating assembly, alsoreferred to as a valve catch. The valve seating assembly may include anouter piston 232, an inner piston 234, a lower spring 236 that biasesthe outer and inner pistons apart, a valve seating pin 240, a seatingdisk 238, and an upper spring 242 that biases the inner piston and theseating disk 238 apart. The outer piston 232 may be adapted to sliderelative to the bore within which it resides, while at the same timeforming a seal with that bore. It is appreciated that some leakage pastthis seal will not affect the operation of the lost motion system 200.The inner piston 234 may be adapted to slide within the outer piston 232to accommodate the formation of a small fluid chamber (where the lowerspring 236 resides) between the two pistons. Slow leakage to and fromthis small fluid chamber may provide for automatic lash adjustmentbetween the slave piston 230 and the valve bridge 310. Accordingly, itis preferable to provide enough leakage space between the inner piston234 and the outer piston 232 to enable automatic lash take up.

The combination of the seating pin 240 and the seating disk 238 may beprovided to decelerate the upward motion of the slave piston andprogressively slow the engine valves 300 as they approach theirrespective seats (not shown). The seating pin 240 may extend into theinner piston 234 at a lower end, and up into the hydraulic circuit 220at an upper end. The seating pin 240 may include one or more sideextensions that check the position of the seating pin relative to theseating disk 238. In an alternative embodiment of the present invention(shown in FIGS. 7 and 8), the seating pin 240 may be fluted toprogressively throttle fluid flow past the seating pin/seating diskinterface to maintain a relatively constant seating force during thelast 1-2 mm before final valve seating. Examples of fluted seating pinsare disclosed in Vanderpoel et al., U.S. Pat. No. 6,474,277 (Nov. 5,2002), which is assigned to the owner of the present application, andwhich is hereby incorporated by reference.

The seating disk 238 may be slidably disposed in the slave piston bore.A small gap may be provided between the seating disk 238 and the slavepiston bore to allow some low level of hydraulic flow around the seatingdisk. The upward movement of the seating disk 238, and the flow aroundits outer edge, may be checked by a shoulder 244 defined by the junctureof the slave piston bore and the hydraulic circuit 220. A gap thatpermits some low level of hydraulic fluid flow may also be providedbetween the interior of the seating disk 238 and the seating pin 240.The upward translation of the seating pin 240 may be arrested as aresult of contact between the upper end of the seating pin and thehousing 202. Contact between the seating pin and the housing mayautomatically set the lash for the system and also provide a valve catchfunction.

By incorporating the valve seating assembly into the slave piston 230,some embodiments of the present invention are able to locate threecomponents affected by hydraulic compliance within a very small space,and thus improve compliance considerations. As a result, variousembodiments of the present invention provide reduced, or even minimized,“dead volume” in the high pressure circuit bounded by the master piston210, the slave piston 230, and the trigger valve 260.

The lost motion system 200 may also include a trigger valve 260. Thetrigger valve 260 may include an internal plunger 262 that is springbiased into a closed or opened position. The bias of the springdetermines whether the trigger valve 260 is normally open, or normallyclosed. Some embodiments of the invention may use either a normally openor a normally closed trigger valve 260. If the trigger valve 260 isnormally closed, for example, it will prevent the release of hydraulicfluid from the hydraulic circuit 220 to the accumulator 250 until it isenergized and opened. This activation may occur rapidly, enabling thehydraulic fluid in the hydraulic circuit 220 to be released andrecharged one or more times per cam revolution.

When the trigger valve 260 is open, hydraulic fluid in the circuit 220is free to flow to the accumulator 250. The accumulator 250 may includean accumulator piston 252 mounted in an accumulator bore 254, anaccumulator spring 256, and a retaining device 258. The retaining device258 may be used to retain the spring 256 such that it biases theaccumulator piston 252 up into the bore 254. The accumulator may berecharged with hydraulic fluid via a feed passage 257. The feed passage257 may optionally include a local check valve provided to prevent theback flow of hydraulic fluid from the accumulator to the feed passage.Hydraulic fluid leakage out of the accumulator 250 may pass through theopening 259 in the retaining device 258. The force of the accumulatorspring 256 may be selected to be less than the force of the valve returnsprings 302 but great enough to rapidly recharge the hydraulic circuit220 when the need arises.

The accumulator 250 may also provide a means for cooling the hydraulicfluid contained in the lost motion system 200. The accumulator piston252 may include a bleed hole extending through its upper surface, or aflattened surface extending along its side wall. The bleed hole orflattened surface may allow a small amount of hydraulic fluid to leakout of the accumulator 250 as it operates. This small amount of leakagemay be constantly replenished with fresh, cool hydraulic fluid from thefeed passage 257. The net effect of this constant leakage andreplenishment is to cool the hydraulic fluid supply in the lost motionsystem 200.

A localized low pressure source of hydraulic fluid may also communicatewith the hydraulic circuit 220. Although not shown in the drawingfigures, it is appreciated that a local source of hydraulic fluid couldcommunicate with the hydraulic circuit 220 through a check valve. Thislocal source of hydraulic fluid could be used to charge the hydrauliccircuit 220 with fluid upon cold start. It is appreciated that thislocal reservoir of hydraulic fluid may be integrated into the housing202.

With continued reference to FIG. 2, the functioning of the system 10 isas follows. As the cam 110 rotates, the follower 124 on the rocker arm120 may follow the surface of the cam, causing the rocker arm to pivotabout the central opening 122. As the rocker 120 pivots, it transfersthe motion of the cam 110 to the push tube 130, which in turn transfersthe motion to the lost motion system 200. When the motion is transferredthrough the lost motion system 200, the valves 300 are actuated toproduce an engine valve event. Any of the foregoing discussed enginevalve events may be provided. The amount of motion transferred from thecam 110 to the valves 300 is controlled by the instantaneous length ofthe lost motion system 200.

The instantaneous length of the lost motion system 200 is controlled bythe trigger valve 260 and the accumulator 250. When the trigger valve260 is in a closed position, hydraulic fluid may first fill (past anoptional check valve that is not shown), and then be retained in thecircuit 220. Hydraulic fluid may fill the circuit 220 when the masterpiston 210 is pushed out of its bore by the spring 212. As the masterpiston 210 moves outward, it may draw fluid into the circuit 220.Additionally, the hydraulic fluid may be pumped into the hydrauliccircuit 220. The fluid in the circuit 220 may cause the outer slavepiston 232 to be pushed downward against the valve bridge 310. As theouter slave piston 232 moves downward, the seating disk 238 may alsomove downward slightly to allow fluid to fill the space between theseating disk 238 and the outer slave piston 232. The seating disk 238may not move downward very far, however, because it is biased upward bythe upper spring 242. The downward movement of the outer slave piston232 may also produce some downward movement of the inner slave piston234 and some relative movement of the seating pin 240. Essentially, theelements of the slave piston that are responsible for controlling valveseating, namely, the seating disk 238, the seating pin 240, and theinner slave piston 234, separate and retain fluid between them. Duringvalve seating, the controlled and limited flow of fluid from the spacesbetween these elements may be used to slow the valve down as theseelements are effectively squeezed together.

After lash between the slave piston and the valve bridge 310 is removed,movement of the master piston 210 (by the cam 110, the rocker 120, andthe push tube 130) is transferred to the slave piston 230 by the lostmotion system 200. As a result, the slave piston 230 moves downward andactuates the valves 300 when the master piston 210 is pushed into itsbore. During this operation, the outer slave piston 232, the inner slavepiston 234, the seating disk 238, and the seating pin 240 essentiallymove together for valve lift events. As long as the trigger valve 260remains closed, the slave piston 230 and the valves 300 may responddirectly to the motion of the master piston 210.

The pumping action of the master piston 210 also helps ensure thathydraulic fluid will seep into the small chamber between the outer slavepiston 232 and the inner slave piston 234 to take up any lash betweenthe slave piston and the valve bridge 310. The self-adjusting lashfeature of the outer and inner slave pistons may compensate for thermalexpansion and contraction of valve train components as well as adjustfor wear of the components over the life of the engine.

If it is desired to lose the motion of any part or whole of any lobe onthe cam 110, then the trigger valve may be opened to decouple the slavepiston 230 from the master piston 210. When the trigger valve 260 isopened, the hydraulic circuit 220 may drain in part to the accumulator250, and the slave piston 230 may be returned by the valve spring 302.All or part of the hydraulic pressure in the hydraulic circuit 220generated by the pumping motion of the master piston 210 may be absorbedby the accumulator 250 and the feed passage 257. As a result, the slavepiston 230 may not be displaced in response to the movement of themaster piston 210, or the slave piston may collapse towards the masterpiston. As the hydraulic fluid in the circuit 220 drains, the force ofthe valve return springs 302 causes the slave piston 230 to be forcedupward. As the outer slave piston 232 moves upward, it acts on the innerslave piston 234 as a result of the trapped fluid between the two. Theupward movement of the outer slave piston 232 also forces fluid past theoutside and the inside of the seating disk 238. The combined upwardmovement of the outer and inner slave pistons, however, forces theseating disk 238 upward against the shoulder 244 due to the bias forceof the upper spring 242. This causes the fluid flow out of the slavepiston bore to be reduced to that flow which can escape through thesmall space between the seating disk 238 and the seating pin 240. Thepin 240 may optionally be provided with flutes (FIGS. 7 and 8) along itssides to facilitate the flow of fluid past it. As a result of theforegoing, the fluid flow out of the slave piston bore is pinched off asthe slave piston 230 indexes upward. This in turn, acts to slow theslave piston 230 down as the engine valves 300 approach their seats.

With continued reference to FIG. 2, it may be particularly desirable todesign the lost motion system 200 such that a failure of the triggervalve 260 always results in an open hydraulic path between themaster-slave piston circuit 220 and the accumulator 250. Trigger valvefailure in the open position may be desirable because the alternative(failure in the closed position) could result in contact between theengine valve 300 and the engine piston (not shown). If the trigger valve260 fails in a closed position, it is not possible to vent the hydraulicfluid from the master-slave circuit 220. As a result, the slave piston230 may experience the full displacement of each lobe on the cam 110. Ifinsufficient lash exists between the slave piston 230 and the valvebridge 310, the full main valve event 112 could cause the slave pistonto travel so far downward that the engine valve 300 risks contacting theengine piston.

Although it is preferred that the trigger valve 260 be designed toremain open during failure, it is appreciated that in an alternativeembodiment of the present invention, the trigger valve 260 could bedesigned to remain closed in the event of a failure.

FIG. 3 shows another embodiment of the present invention in which likereference characters refer to like elements. The embodiment shown inFIG. 3 differs from that shown in FIG. 2 in that it does not incorporatevalve seating elements into the slave piston 230. The solid slave piston230 is biased downward by a spring 231. Depending upon its strength, thespring 231 may provide some valve seating counter-force. It isappreciated that other valve seating elements may be connected to thehydraulic circuit 220, or not, as the case may be, in alternativeembodiments of the invention.

FIG. 5 shows yet another embodiment of the present invention, in which ahardened cup 246 may be pressed into the housing 202 above the seatingpin 240. The hardened cup 246 may be used to cushion any impact that mayoccur between the seating pin 240 and the interior of the housing 202.The cup 246 may be considered “hard” as compared with the material fromwhich the housing 202 is constructed. Use of the hardened cup 246 mayallow use of a relatively softer material for the housing 202, therebymaking the housing easier and less expensive to machine. It isunderstood that the hardened cup 246 is not necessary for allembodiments of the inventions, but rather that it is an optionalcomponent that may be desirable in certain circumstances.

FIG. 6 is a schematic cross-sectional view of the region surrounding alower portion of a slave piston 230 such as those shown in FIGS. 2, 3,5, 7, and 9, with the addition of a bleeder braking hydraulic plunger239. An example of the bleeder braking valve actuation that may beprovided is illustrated in FIG. 14. Bleeder braking may be accomplishedby cracking open one or more exhaust valves so that they are openthroughout much or all of the engine cycle during an engine brakingmode. As a result, exhaust gas bleeds out of the cylinder into theexhaust manifold during each exhaust and compression stroke. Enginenoise associated with bleeder braking may be reduced as compared withthat produced by compression-release braking. Bleeder braking may beenhanced when conducted in conjunction with an exhaust restrictiondevice.

With continued reference to FIG. 6, the bleeder braking hydraulicplunger 239 is disposed in a lower housing cavity 248. The hydraulicplunger 239 may be slidably retained in the lower housing cavity 248 bya plunger stop 249. The plunger stop 249 may be a ring snapped into thewall of the housing 202. A low pressure hydraulic feed 245 may providehydraulic fluid to the housing cavity 248 to actuate the hydraulicplunger 239. A hydraulic control valve may be used to control the supplyof fluid to the feed 245. When the control valve is actuated, hydraulicfluid may fill the cavity 248 and lock the hydraulic plunger 239 intoits lowermost position. When the control valve is de-actuated, the fluidin the cavity 248 may drain back through the feed 245. The spring 247may assist in retracting the hydraulic plunger back into the cavity 248when the control valve is de-actuated.

During ordinary (non-bleeder brake mode) operation of the lost motionsystems 200 shown in FIGS. 2, 3, 5, 7, and 9, the bleeder brakehydraulic plunger 239 may be fully collapsed into the lower housingcavity 248. During this time valve actuation occurs in response to themaster-slave piston motion.

Hydraulic fluid may be released from the master-slave circuit 220 whenbleeder braking is desired. Release of fluid from the master-slavecircuit 220 may cause the outer slave piston 232 to collapse into itsbore. Hydraulic fluid may be supplied from the low pressure feed 245 tothe housing cavity 248 causing the hydraulic plunger 239 to extenddownward. In turn, the downward extension of the hydraulic plunger 239may crack open one or more exhaust valves so that bleeder brakeoperation begins. When cessation of bleeder braking is desired,provision of hydraulic fluid from the low pressure feed 245 may bediscontinued, allowing the hydraulic plunger 239 to again collapse intothe housing cavity 248.

Another alternative embodiment of the invention is shown in FIG. 7 inwhich the master piston bore extends over the slave piston bore. Thepositioning of the master piston bore over the slave piston bore mayfurther enhance the systems compactness. As shown, a short hydraulicpassage may connect the master piston bore to the slave piston bore. Themaster piston 210 may partially occlude the short hydraulic passage whenthe master piston is at its deepest position in its bore.

The lost motion system 200 shown in FIG. 7 also includes a stop 500 forselectively limiting the range of motion of the accumulator piston 252relative to the bore 254. This embodiment of the invention may beparticularly useful when the trigger valve 260 is designed to remainopen in the event it fails. The operation of the stop 500 may providethe lost motion system 200 with the capability of providing some levelof valve actuation in the event that the trigger valve 260 fails (i.e.,a failure mode of operation).

The stop 500 may include an elevated surface 510 and a depressed surface520. The elevated and depressed surfaces may be adapted to selectivelylimit the downward travel of the accumulator piston 252, therebylimiting maximum accumulator volume. When the depressed surface 520 ispositioned below the accumulator piston 252, as shown in FIG. 7, theaccumulator piston may be free to move through the full range of motionrequired for operation of the lost motion system in a non-failure mode.

During a failure mode, the stop 500 may be moved so that the elevatedsurface 510 is positioned below the accumulator piston 252. The elevatedsurface 510 may hold the accumulator piston 252 in an elevated position,such that the fluid volume of the accumulator 250 is reduced. Reductionof the accumulator volume may allow the master piston 210 to becomehydraulically locked with the slave piston 230 even when the triggervalve 260 fails in an open position. The height of the elevated surface510, and thus the elevated position of the accumulator piston 252, maybe selected so that the slave piston provides only a reduced level ofvalve actuation (e.g., main intake or main exhaust), or a full level ofvalve actuation, when the trigger valve fails in an open position. Inthis manner, the stop 500 may provide the lost motion system 200 withthe ability to operate at a reduced level of efficiency so as to “limphome” for repair of the trigger valve.

It is appreciated that the stop 500 may take any number of forms otherthan that shown in FIG. 7, which is intended to be exemplary only. Thestop 500 need only perform the function of selectively fixing the lowermost position of the accumulator piston 252 so that the maximumaccumulator volume is reduced during a failure mode. The stop functionmay be provided by any suitable mechanical, electric, hydraulic,pneumatic, or other means.

The embodiment of the present invention shown in FIG. 7 also includesvalve seating elements that differ slightly from those shown in FIGS. 2,3, and 5. FIG. 8 is an enlarged view of the valve seating elements shownin FIG. 7. The valve seating elements may include an inner slave piston234, a seating disk 238, a seating pin 240, an upper spring 242, and ahardened cup 246. The valve seating elements are shown in the positionattained when the engine valve 300 is closed or seated. The seating pin240 is disposed between the inner slave piston 234 and the hardened cup246. The seating pin 240 may move up and down with the inner slavepiston 234. The seating disk 238 may be spring biased against thehardened cup 246. One or more flutes may be provided on the seating pin240 to throttle fluid flow between the seating pin and the seating disk238 as the seating pin approaches the harden cup 246. The hardened cup246 may be pressed into the housing and provided with an off-centeropening designed to throttle fluid flow past the cup during engine valveclosing.

Another alternative embodiment of the present invention is illustratedby FIG. 9. The embodiment shown in FIG. 9 is similar to the embodimentshown in FIG. 7. In FIG. 8, an additional design feature may prevent theslave piston 230 from extending past a preset lower limit. In thisembodiment of the invention, a clipping port 204 may be incorporatedinto the wall of the slave piston bore. A clipping passage 206 mayconnect the clipping port 204 to the accumulator 250. Each time theslave piston 230 travels sufficiently downward that the upper edge ofthe slave piston clears the clipping port 204, the high pressurehydraulic fluid in the master-slave circuit 220 may drain through theclipping passage 206 to the accumulator 250. This effectively limits or“clips” the downward travel of the slave piston 230. Selective placementof the clipping port 204 relative to the dimension of the slave piston230 may prevent over travel of the slave piston and the engine valve300.

The embodiment of the invention shown in FIG. 9 may be particularlyuseful to carry out early exhaust valve opening during positive poweroperation of the system. Early exhaust valve opening is illustrated inFIG. 16 by exhaust valve motion 606. Early exhaust valve opening may beused to stimulate turbocharger boost, particularly at low engine speeds.This may produce improved low speed engine torque.

With reference to FIGS. 9 and 16, early exhaust valve opening may beachieved by providing an exhaust cam 110 with an enlarged main exhaustlobe. The enlarged main exhaust lobe causes the master-slave pistoncombination to actuate the exhaust valve 300 at an earlier time in theengine cycle than it otherwise would. As a result, the exhaust valve 300runs the risk of extending farther into the engine cylinder than itotherwise would, and potentially impacting the engine piston in thecylinder. The clipping port 204 and clipping passage 206 may preventover travel of the exhaust valve 300 by limiting the extension of theslave piston 230 out of the bore in which it is disposed.

When it is desired to have normal exhaust valve actuation, as opposed toearly exhaust valve actuation, the lost motion system 200 may beoperated to provide a centered lift motion, illustrated in FIG. 11.Centered lift of the exhaust and intake valves is illustrated by mainexhaust event 602 and main intake event 702. As compared with aconventional exhaust event 600 and a conventional main intake event 700,shown in FIG. 10, the centered lift motions in FIG. 11 begin later, endsooner, and have a reduced lift. The centered lift motions may beachieved by maintaining the trigger valve for the lost motion systemopen as the master piston begins to move under the influence of the mainevent lobe on the cam. Maintaining the trigger valve open during part ofthe main event lobe allows some hydraulic fluid that would normally beused to displace the slave piston to flow to the accumulator instead.After the trigger valve is closed part way through the main event, theslave piston resumes following the motion prescribed by the main eventlobe on the cam. The slave piston displacement, and thus the enginevalve motion, is delayed and reduced in magnitude, however, becausethere is less hydraulic fluid in the master-slave circuit.

Early intake valve closing and main exhaust actuation for positive poweroperation is illustrated in FIG. 12. The main intake event 704 endssooner than the corresponding main intake event 700 shown in FIG. 10,and accordingly is referred to as early intake closing. The early intakevalve closing may be accomplished by releasing high pressure hydraulicfluid from the master-slave circuit of a lost motion system before themaster piston has completed the motion prescribed by the main intakelobe on the cam associated with the master piston. The release of thisfluid may cause the slave piston and engine valves to collapse beforethe master piston returns them under the influence of the cam.

With reference to FIG. 13, various engine valve actuations, andmodifications thereof, that may be provided using the various system andmethod embodiments of the invention are shown. For example, an earlyintake closing event 704 is shown to be carried out with an optionalintake valve EGR event 710 and an optional exhaust valve EGR event 620.The foregoing valve motions are intended to be exemplary. It isappreciated that the various system embodiments of the present inventionmay be used to carry out a wide variety of different valve events havingvariable timing and lift.

With reference to FIG. 15, the various embodiments of the invention maybe used to provide compression-release engine braking events 640 incombination with optional exhaust gas recirculation (“EGR”) events 650.The main intake event 700 may provide auxiliary exhaust lift cylindercharging for engine braking.

For example, the foregoing embodiments of the invention may be used toreduce the “shake” commonly associated with diesel engines as they areshut down. The variable valve actuation system may be used to shut downthe valve actuation in individual engine cylinders, one at a time,thereby reducing the shake that occurs when all cylinders are shut downsimultaneously.

With reference to FIG. 17, in an alternative embodiment of the presentinvention, valve actuation may be provided primarily or secondarilythrough a lost motion system 200. A rocker arm 120 may receive motionfrom a motion imparting device, such as but not limited to a cam 110. Asthe rocker arm 120 encounters lobe(s) on the cam 110, it may pivot aboutthe rocker shaft 122 and engage the lost motion system 200. The lostmotion system 200 may generally be comprised of a master piston 210 anda slave piston 230. A means for imparting motion 100, such as the rockerarm 120, may contact and drive the master piston 210. This contact maybe direct or it may be through an intermediate component, such as butnot limited to, a push tube 130. The master piston 210 may be disposedin a bore 204 in a housing 202, such that the master piston 210 mayslide within the bore 204 while maintaining an effective seal with thebore 204. The bore 204 in which the master piston 210 resides may behydraulically connected to a second bore 206, in which the slave piston230 may reside. The slave piston 230 may be disposed in the second bore206 so that it may slide within the second bore 206 while maintaining aneffective seal with the second bore 206.

The hydraulic circuit between the master piston 210 and the slave piston230 (the master-slave circuit) may be selectively filled with hydraulicfluid under the control of valve 260 through conduit 220. Motionimparted to the master piston 210 by the rocker arm 120 may betransferred to the slave piston 230 and the engine valves 300 when themaster-slave circuit is provided with sufficient fluid. Hydraulic fluidsupply to and from the master-slave circuit may be provided at highspeed when the valve 260 is a trigger valve. The use of a trigger valveto add and drain fluid from the master-slave circuit may permit highspeed variable valve actuation.

In the embodiment shown in FIG. 17, the means for imparting motion 100for the valve actuation system 10 may be equipped with an additionalvariable valve actuation feature. The additional VVA feature may berealized using a rocker arm 120 with an extension 121. The extension 121may protrude from the rocker arm 120 and terminate in a head adjacent tothe valve bridge 310, or an engine valve 300. A lash space may beprovided between the extension arm 121 and the valve bridge 310. A slotmay be provided in the slave piston 230 in order to receive theextension 121. The slot may be of sufficient size that the slave piston230 and the extension 121 may move freely relative to one anotherwithout interference.

The additional VVA feature in the form of the extension 121 may be usedto provide late valve opening and early valve closing when the extension121 is used to actuate the engine valves 300 instead of the lost motionsystem 200. The designation of the extension 121 providing “late” valveopening and “early” valve closing is in comparison to the opening andclosing times provided by the lost motion system 200 and is a functionof there being a greater lash space between the extension 121 and thevalve bride 310 then between the slave piston 230 and the valve bridge310 as well as a function of the respective rocker ratio for theextension 121 and the effective rocker ratio for the slave piston 230.

The additional VVA provided by the extension 121 may be provided byeither maintaining the valve 260 in an “open” position throughout thevalve event or by selectively opening the valve 260 during the valveevent. When the valve 260 is maintained open throughout the valve event,fluid is not trapped in the master-slave circuit, the motion of themaster piston 210 is not transferred to the slave piston 230, and thevalves 300 are actuated solely by the motion of the extension 121. Whenthe valve 260 is selectively opened during the valve event only earlyvalve closing is provided because normal valve opening is provided bythe lost motion system 200 and early valve closing is provided by theextension 121.

The extension 121 may also provide a fail-safe mode of operation for theembodiment of the present invention shown in FIG. 17 in the event thatthe desired amount of hydraulic fluid needed for valve actuation usingthe lost motion system 200 is not maintained in the master-slavecircuit. The lack of fluid in the master-slave circuit can be for anyreason, such as a failure of the valve 260. In such an event, the motionimparted by the rocker arm 120 to the lost motion system 200 will not beeffectively transferred to the engine valves 300. However, the motion ofthe rocker arm 120 about the rocker shaft 122 inherently causes theextension 121 to rotate about the rocker shaft as well. As a result, themotion of the extension 121 that exceeds the lash space between it andthe valve bridge 310 may be transferred to the valve bridge 310 andvalves 300, should the lost motion system 200 become inoperative. Thehydraulic ratio of motion transferred from the master piston 210 to theslave piston 230 may be set such that the extension 121 does not “catchup” with the valve bridge 310 when it is actuated by the slave pistonduring non-failure mode. It may be only when the lost motion system 200fails that the motion of the extension 121 is transferred to the valvebridge 310.

With reference to FIG. 18, in another embodiment of the valve actuationsystem 10, the lost motion system may also include a valve-catchsubsystem to aid in slowly seating the one or more engine valves 300.The valve-catch subsystem shown in FIG. 18 is further illustrated inFIG. 20.

With reference to FIG. 20, the slave piston 230 may incorporate a valveseating assembly, also referred to as a valve catch. The valve seatingassembly may include an outer piston 232, an inner piston 234, a lowerspring 236 that biases the outer and inner pistons apart, a valveseating pin 240, a seating disk 238, an upper spring 242 that biases theinner piston and the seating disk 238 apart, and a valve closing disk249 biased upward by a spring. The outer piston 232 may be adapted toslide relative to the bore within which it resides, while at the sametime forming a seal with that bore. It is appreciated that some leakagepast this seal may not affect the operation of the lost motion system200. The inner piston 234 may be adapted to slide within the outerpiston 232 to accommodate the formation of a small fluid chamber (wherethe lower spring 236 resides) between the two pistons. Slow leakage toand from this small fluid chamber may provide for automatic lashadjustment between the slave piston 230 and the valve bridge 310.Accordingly, it is preferable to provide enough leakage space betweenthe inner piston 234 and the outer piston 232 to enable automatic lashtake up.

The combination of the seating pin 240 and the seating disk 238 may beprovided to decelerate the upward motion of the slave piston andprogressively slow the engine valves 300 as they approach theirrespective seats (not shown). The seating pin 240 may extend into theinner piston 234 at a lower end, and up into the hydraulic circuit 220at an upper end. The seating pin 240 may include one or more sideextensions that check the position of the seating pin relative to theseating disk 238. In an alternative embodiment of the present invention(shown in FIGS. 7 and 8), the seating pin 240 may be fluted toprogressively throttle fluid flow past the seating pin/seating diskinterface to maintain a relatively constant seating force during thelast 1-2 mm before final valve seating. Examples of fluted seating pinsare disclosed in Vanderpoel et al., U.S. Pat. No. 6,474,277 (Nov. 5,2002), which is assigned to the owner of the present application, andwhich is hereby incorporated by reference.

The seating disk 238 may be slidably disposed in the slave piston bore.A small gap may be provided between the seating disk 238 and the slavepiston bore to allow some low level of hydraulic flow around the seatingdisk. The upward movement of the seating disk 238, and the flow aroundits outer edge, may be checked by a catch-cap 244 disposed at thejuncture of the slave piston bore and the hydraulic circuit 220. A gapthat permits some low level of hydraulic fluid flow may also be providedbetween the interior of the seating disk 238 and the seating pin 240.The upward translation of the seating pin 240 may be arrested as aresult of contact between the upper end of the seating pin and thehousing 202. Contact between the seating pin and the housing mayautomatically set the lash for the system and also provide a valve catchfunction.

When the trigger valve 260 is closed, hydraulic fluid may be containedbetween the seating disk 238 and the valve closing disk 249. As theengine valve begins to close, the slave piston 232 is pushed into thebore 206. This may cause the seating disk 238 and the valve closing disk249 to be forced towards the master piston 210. As the valve closingdisk 249 moves towards the master piston, it may contact the housing202, which may terminate the upward translation of the valve closingdisk 249. When the valve closing disk 249 contacts the housing 202, iteffectively prevents hydraulic fluid from flowing back to the masterpiston. The hydraulic fluid may be trapped between the valve closingdisk 249 and the slave piston 234, thereby preventing the valve fromseating. In order to allow the valve to seat, the trigger valve 260 maybe opened, allowing the hydraulic fluid to escape. In this manner, alate valve closing may be accomplished. If the trigger valve 260 isopen, hydraulic fluid may not be contained between the seating disk 238and the valve closing disk 249, and normal valve closing may occur. Agraph illustrating a late closing valve profile may be seen at FIG. 21.

FIG. 19 shows an alternative embodiment of the valve actuation system10. With continued reference to FIG. 19, the valve actuation system 10is generally comprised of a first rocker arm 120, a second rocker arm140, a lost motion system 200, and at least one engine valve 300.

A first portion of the first rocker arm 120 may contact a motionimparting device 110, such as but not limited to a cam, directly orthrough an intermediate device, such as but not limited to a roller orcam follower 127A. A second portion 128 of the rocker arm 120 maycontact the lost motion system 200, either directly or through anintermediate device, such as but not limited to a pushtube 130. A thirdportion 129 of the rocker arm 120 may contact the second rocker arm 140directly or through an intermediate device, such as but not limited to apin or roller 129A.

The second rocker arm 140 may be mounted coaxially with the first rockerarm 120 on the rocker shaft 123. The second rocker arm 140 may have anactuation end 141 disposed between the lost motion system 200 and theone or more engine valves 300. The actuation end 141 may contact the oneor more engine valves 300 directly or through an intermediate component,such as but not limited to a valve bridge 310. The actuation end 141 ofthe second rocker arm 140 may also be in contact with the third portion129 of the first rocker arm 120. These components may be separated by alash distance, between the third portion 129 of the first rocker arm 120and the actuation end 141 of the second rocker arm 140. This lash mayenable the first rocker arm 120 to rotate to a certain degree beforecontacting, and thus actuating, the second rocker arm 140. This delay inactuation may cause a delayed engine valve opening.

The lost motion system 200 may generally be comprised of a master piston210 and a slave piston 230. The master piston 210 may be disposed in abore 204 in a housing 202, such that the master piston 210 may slidewithin the bore 204 while maintaining an effective seal with the bore204. The bore 204 of the master piston 210 may be hydraulicallyconnected to a second bore 206, in which the slave piston 230 mayreside. The slave piston 230 may be disposed in the second bore 206 sothat it may slide within the second bore 206 while maintaining aneffective seal with the second bore 206. The slave piston 230 may bedisposed so that if the hydraulic circuit between the master piston 210and the slave piston 230 is filled with hydraulic fluid, any motion ofthe master piston 210 into the bore 230, caused by the second portion128 of the first rocker arm 120, may be transferred to the slave piston230.

The slave piston 230 may act through the actuation end 141 to actuatethe one or more engine valves 300 or intermediate device. Hydraulicfluid may be supplied to the hydraulic circuit between the master piston210 and the slave piston 230 via a hydraulic conduit 220. Control of thehydraulic fluid supply from the hydraulic conduit 220 may be provided bya valve 260, which may be, but is not limited to, a trigger valve orsolenoid valve.

Because of the lash between the third portion 129 of the first rockerarm 120 and the actuation end 141 of the second rocker arm 140, themotion transferred to the one or more engine valves 300 is provided onlythrough the lost motion system 200. The rotation of the first rocker arm120 does not cause actuation of the second rocker arm 140 because of thelash distance between each rocker arm. Instead, valve actuation motionis provided through the first portion 128 of the first rocker arm 120 tothe lost motion system 200, which then actuates the one or more enginevalves 300.

If the valve 260 fails in an open position, motion will not effectivelybe transferred from the master piston 210 to the slave piston 230.Without the necessary engine valve 300 actuation, engine failure mayresult. However, in the fail safe system 100 shown in FIG. 19, theengine valves 300 may still be actuated in the event of a hydraulicvalve 260 failure by the second rocker arm 140. When the first rockerarm 120 receives motion from the motion imparting device 110, the firstrocker arm 120 may rotate in a clockwise direction. As the first rockerarm 120 rotates, the third extrusion 129 may contact the second rockerarm 140. The second rocker arm 140 may thus be forced to also rotate ina clockwise direction. As the second rocker arm 140 rotates, the arm 141may contact the one or more engine valves 300 or intermediate component,thereby actuating the one or more engine valves 300.

It is also possible for the VVA valve 260 to fail in a closed position,thereby maintaining fluid in the hydraulic circuit. This may cause theengine valves 300 to be held in an open position. If the engine valves300 are held in an open position, there is a risk of valve or enginedamage due to contact between the valves and the piston. Such contactwould occur at approximately a top dead center (TDC) position. Anotherembodiment of the fail-safe system 100, depicted in FIG. 19 may preventthis possible valve and/or engine damage.

It will be apparent to those skilled in the art that variations andmodifications of the present invention can be made without departingfrom the scope or spirit of the invention. For example, the componentsand arrangement of the lost motion system 200, as shown in FIGS. 2, 3,5, 7, 9, 16, 17 and 18 are for exemplary purposes only. It iscontemplated that other components necessary for a properly operatinglost motion system may be provided and that the arrangement of themaster piston, the slave piston, the trigger valve, and the accumulator,may vary depending on a variety of factors, such as, for example, thespecification of the engine. Thus, it is intended that the presentinvention cover all such modifications and variations of the invention,provided they come within the scope of the appended claims and theirequivalents.

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 57. A valve actuation system comprising: a lost motion systemhaving a master piston bore and a slave piston bore, wherein the masterpiston bore and the slave piston bore intersect, a master pistonslidably disposed in the master piston bore, wherein the master pistonis adapted to receive an input motion, and a slave piston slidablydisposed in the slave piston bore, wherein the slave piston is adaptedto actuate one or more engine valves; and a rocker arm having a firstcontact portion adapted to provide input motion to the master piston anda second contact portion adapted to provide selective actuation for theone or more engine valves.
 58. The system of claim 57 further comprisingan engine valve bridge disposed between the one or more engine valvesand the second contact portion.
 59. The system of claim 57 wherein alash space is selectively provided between the second contact portionand the one or more engine valves.
 60. The system of claim 57 whereinthe lost motion system further comprises: a hydraulic supply passagecommunicating with the slave piston bore; and a trigger valveoperatively connected to the hydraulic supply passage.
 61. The system ofclaim 57 wherein the slave piston further comprises means for seatingthe one or more engine valves.
 62. The system of claim 61 wherein themeans for seating further comprises means for selectively preventing theone or more engine valves from seating.
 63. The system of claim 57wherein the slave piston further comprises a valve seating assembly. 64.The system of claim 63 further comprising: a trigger valve; and ahydraulic passage extending between the trigger valve and the valveseating assembly.
 65. The system of claim 64 further comprising: ahydraulic fluid supply passage communicating with the master pistonbore; and a check valve disposed in the hydraulic fluid supply passage.66. The system of claim 60 wherein the trigger valve is adapted toprovide high speed actuation.
 67. The system of claim 60 furthercomprising a fluid accumulator in hydraulic communication with thetrigger valve.
 68. The system of claim 57 wherein the master piston boreand the slave piston bore extend in directions substantiallyperpendicular to each other.
 69. The system of claim 62 wherein themeans for selectively preventing the one or more engine valves fromseating further comprises means for providing bleeder braking.
 70. Avalve actuation system comprising: a lost motion system having a masterpiston bore and a slave piston bore, wherein the master piston bore andthe slave piston bore extend axially in directions substantiallyperpendicular to each other, a master piston slidably disposed in themaster piston bore, wherein the master piston is adapted to receive aninput motion, and a slave piston slidably disposed in the slave pistonbore, wherein the slave piston is adapted to actuate one or more enginevalves; and a rocker arm having a first contact portion adapted toprovide input motion to the master piston and a second contact portionadapted to selectively actuate the one or more engine valves.
 71. Thesystem of claim 70 further comprising an engine valve bridge disposedbetween the one or more engine valves and the second contact portion.72. The system of claim 70 wherein a lash space is selectively providedbetween the second contact portion and the one or more engine valves.73. The system of claim 70 wherein the lost motion system furthercomprises: a hydraulic supply passage communicating with the slavepiston bore; and a trigger valve operatively connected to the hydraulicsupply passage.
 74. The system of claim 70 wherein the slave pistonfurther comprises means for seating the one or more engine valves. 75.The system of claim 74 wherein the means for seating further comprisesmeans for selectively preventing the one or more engine valves fromseating.
 76. A method of providing variable valve actuation for aninternal combustion engine valve comprising the steps of: actuating theengine valve for a valve event during at least a positive power mode ofengine operation using a lost motion system; discontinuing actuating theengine valve for the valve event during at least a positive power modeof engine operation using the lost motion system; and actuating theengine valve for the valve event during at least a positive power modeof engine operation using a rocker arm.
 77. The method of claim 76wherein the step of discontinuing actuating the engine valve isresponsive to a failure in the lost motion system.
 78. The method ofclaim 76 wherein the step of discontinuing actuating the engine valve isresponsive to selective deactivation of the lost motion system.
 79. Themethod of claim 76 further comprising the step of providing a loweramount of lift for the valve event using the rocker arm as compared tothe amount of lift provided for the valve event using the lost motionsystem.
 80. The method of claim 76 further comprising the step ofproviding different valve event timing using the rocker arm as comparedto the valve event timing provided using the lost motion system.
 81. Thesystem of claim 57 further comprising: a second rocker arm disposedadjacent to the rocker arm, said second rocker arm having a rocker shaftreceiving end, an actuation end, and an intermediate portion between therocker shaft receiving end and the actuation end, wherein the rocker armsecond contact portion selectively contacts the second rocker armintermediate portion, and the second rocker arm actuation end isdisposed between the slave piston and the one or more engine valves. 82.The system of claim 57 further comprising: a second rocker arm disposedadjacent to the rocker arm, said second rocker arm having a rocker shaftreceiving end, an actuation end, and an intermediate portion between therocker shaft receiving end and the actuation end, wherein the rocker armsecond contact portion selectively contacts the second rocker armintermediate portion, and the second rocker arm actuation end isdisposed between the slave piston and a valve bridge associated with theone or more engine valves.